1. Field of the Invention
The present invention relates to a printing apparatus and a printing method by which a printing head having a plurality of printing elements that can apply color material to a printing medium can be used to print an image by a plurality of printing modes.
2. Description of the Related Art
As an ink jet printing apparatus, a serial-type printing apparatus has been used that uses a printing head in which many nozzles (printing elements) including ejection ports and liquid paths are arranged to print an image. In the serial-type printing apparatus, an image is printed on a printing medium by alternately repeating the printing scanning in the main scanning direction of the printing head and the transport operation of the printing medium in the sub-scanning direction. In the printing apparatus as described above, such an image printing is required that is stable in various factors such as color formation, gradation, and uniformity. The image uniformity in particular is easily influenced by factors caused in the step of manufacturing a printing head such as a slight variation among nozzles or the dirt around the ejection ports of the respective nozzles. Owing to the variation among the nozzles as described above, there is a possibility that the amount of ink ejected through the respective nozzles or the ejection directions therefrom are unstable, thus density unevenness of a printed image may be caused. When a so-called multipath printing method is used according to which a single printing region is printed by a plurality of scannings by a printing head, a printed image can be prevented from having uneven density by reducing the influence by the variation among the nozzles. However, the use of the multipath printing method as described above causes a declined printing speed due to the increased number of scannings by the printing head. In recent years, such a printing apparatus has been generally used that has a plurality of printing modes so as to be able to select one path printing method or a printing operation using a multipath printing method having a reduced number of paths, and a printing operation using a multipath printing method having an increased number of paths. In the printing apparatus as described above, a user can select a printing method depending on an image quality and a printing speed.
In the case of a multipath printing method such as a 4-path printing method, four mask patterns having a complementary relationship to one another are generally used to thin out a printed image. Each of these four mask patterns has a 25% culling rate (printing rate). Thus, a 100%-image is printed through four printing scannings based on the printing data thinned-out by the four mask patterns.
Japanese Patent Laid-Open No. 2005-177992 discloses a printing apparatus that uses mask patterns having not-equal printing rates. For example, a mask pattern corresponding to nozzles at both ends of a nozzle array has a lower printing rate and a mask pattern corresponding to a nozzle at one end of the nozzle array has an increased printing rate. Thus, when such a mask pattern is used that has printing rates that are not equal and that are uneven, there is a possibility that a nozzle part corresponding to the mask pattern having a high printing rate has a high number of ink ejections and thus the nozzle part may be deteriorated sooner than in the case of other nozzles. To prevent this, in Japanese Patent Laid-Open No. 2005-177992, another mask pattern having printing rates that are uneven in an inverted manner is prepared. Thus, the two mask patterns are alternately used depending on each printing scanning to supprese the early deterioration of a specific nozzle. For example, when one mask pattern has a high printing rate corresponding to the nozzle at an end of the nozzle array, the other test pattern is arranged to have a low printing rate corresponding to the nozzle at the end of the nozzle array so that these test patterns are alternately used depending on each printing scanning.
Image printing modes in a printing apparatus include a mode in which a nozzle to be used (to-be-used nozzle) and a nozzle not to be used (not-to-be-used nozzle) are fixedly set in a nozzle array. For example, two nozzle arrays in the printing head are divided those nozzles in an upstream-side half region in the transport direction of the printing medium (upstream-side nozzles) and those nozzles in a downstream-side half region in the transport direction (downstream-side nozzles). Then, during the first printing scanning by the printing head, the first ink is ejected through the upstream-side nozzles in one of the two nozzle arrays. Then, during the second printing scanning after the transport operation of the printing medium, the second ink is ejected through the downstream-side nozzles of the other nozzle array so as to coat the printing region applied with the first ink. When not-to-be-used nozzles are fixedly set in the nozzle array as described above, such a mask pattern cannot be used that has an inverted printing rate for each printing scanning. Thus, a to-be-used nozzle and a not-to-be-used nozzle cannot have a similar deterioration level among the nozzles in the respective nozzle arrays.
When the printing mode where a not-to-be-used nozzle is fixedly set and the printing mode where a not-to-be-used nozzle is not fixedly set are carried out in one printing apparatus, a difference in the deterioration among nozzles caused by the former printing mode has an influence on the latter printing mode. Specifically, a difference in the deterioration among nozzles caused by the former printing mode causes the resultant imaged by the latter printing mode to have not-uniform qualities, thus there is a possibility the uniformity is damaged.